It’s the Friday Puzzle!

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First, I am delighted that my new magic trick has been launched! It is called The Grid, and allows anyone to look like a mathematical genius. Details here.

OK, to the puzzle. Please do NOT post your answers, but do say if you think you have solved the puzzles and how long it took. Solution on Monday.

Imagine that you have the following three bowls:

Bowl A has an 8 liter capacity, and contains 5 liters of water.
Bowl B  has a 5 liter capacity and contains 3 liters of water.
Bowl C has a 3 liter capacity and contains 2 liters of water.

Can you measure exactly 1 liter, pouring only 2 times?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle(UKhere and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

82 comments on “It’s the Friday Puzzle!

  1. tomhickling says:

    Got it in 30 secs

  2. Bob says:

    Using your US dictionary today Richard?

  3. Thicko says:

    Yes.

  4. Canadian Atheist says:

    Does “measure” mean having a bowl containing just one liter (or even litre) of water?

  5. Yay got it😀 I think I saw a similar one somewhere years ago that’s why so quickly, prob like 1 min

    • Adzcliff says:

      If you’ve seen Die Hard 3, you would’ve seen Bruce Willis and Samuel L. Jackson’s characters arguing over a similar version. But anyway, this is a distraction, still working on it…

    • Mark_D says:

      “Measure” is vague and presents multiple ‘trick’ solutions. But there is at least one way to end up with 1L in a bowl without any funny business.

    • Stevie says:

      In Die Hard with a Vengence, the principal heroes had to place a vessel containing exactly 4 pints (or litres, whichever it was) measuring the four pints using only a 5 pint and a 3 pint vessel. There was no limit to the number of pourings but the 4 pints had to be placed on a digital scale to deactivate a bomb.

  6. Selim says:

    Bad score; Solved it in 1minute

  7. dcmonk79 says:

    If you assume uniform shape of bowl then just 1 pour is needed.

  8. sinaidi says:

    i solved the puzzel

  9. Andy Jackson says:

    Done! My brain cell is working this week!

  10. Anonymous says:

    Yes, solved once I read the puzzle properly!

  11. Anonymous says:

    Got it. about 1-2 minutes.

  12. One Eyed Jack says:

    Too easy Drill Sargent!

  13. hanry_m says:

    2.5 min…. but hey, some people are a bit slower…

  14. mightyhero says:

    I figured out how to do it.

  15. Alistair says:

    3 of us have been discussing this for 10 minutes and we can’t get it! Although we have found a wrong solution involving no pours at all.

    • Leann Rimes says:

      I’ve got the cheat answer with no pours as well…

      Can’t do the proper one though… I know it’s a good puzzle when it starts to get me worked up!

    • Alistair says:

      Just looked at it again and got it. How on earth did we miss that?!?!

  16. H says:

    I think it is possible in one move

  17. Phil H says:

    I can relax for the day now. All solved in 1 minute.

  18. vicinca says:

    About a minute, too.

  19. Andy Jackson says:

    Or imagine you work in a colonic irrigation centre

    Bowel a contains 3 litres…

  20. ctj says:

    two solutions. the solution richard is not expecting took a couple of minutes, and then the expected solution took a few seconds.

  21. Stan says:

    Darn it too me two minutes, but it was fun to think outside the box a little. I’m impressed with the speedier folks.

  22. safc4ever says:

    Put a lid on Bowl C and you have 1 liter (sic) of air! – No pouring.

    I know we are asked not to give our answers, but I assume that this is not the desired solution, as we are expected to think of water volume.

  23. Natura Umana says:

    Does pouring means pouring outside of the bowl or pouring from one bowl to another?

  24. Lazy T says:

    Simpel.

  25. Berhard says:

    about one minute

  26. Frederick Forsyth says:

    I couldn’t do it so I Googled it just to get it out of my head. If Richard’s answer is the same as the one I found (quizzes for kids website!) then people are going to be WELL unhappy on Monday morning.

  27. mittfh says:

    I’ve seen similar puzzles before, so about a minute of mental simulations and I arrived at what’s likely to be the correct answer. Unlike some similar puzzles, this one retains all ten litres of water without disposing of any.

    Oh, and of course with Richard not explicitly specifying what we’re measuring one litre of, I also arrived at the “no pours” joke answer🙂

  28. The straightforward non-lateral thinking version (the only operations allowed are “pour the whole contents of one bowl into another or on the ground”, and the end condition is “one of the bowls containing exactly one liter”) is provably unsolvable in 2, easy in 3. I can think of one lateral solution that only takes one pour. I haven’t thought of the apparently intended 2-pour lateral solution yet.

    • ivan says:

      I agree that there seems to be no “proper” solution in 2 pours. The lateral solutions I can think of rely upon the bowls themselves being of negligible volume, which doesn’t seem to be consistent with the stipulation “exactly”.

    • Keith Twatt says:

      There is definitely a proper solution in two pours. It only took me four hours to get it🙂

    • Ken Haley says:

      I’d love to see your “unsolvable” proof, because the correct answer is straightforward–following all your rules of operations. You’re just missing it.

    • ivan says:

      I have exhaustively tested all of the true 2-pour solutions. There’s only 9 possible first moves, and none of them present an option for completion with another pour. Though I’ve now found a trick solution that doesn’t have the problem I mentioned earlier, but goes beyond that list of 9 simple first pours. So it’s all a question of what you allow to be called a pour.

    • ivan says:

      Actually, I now realise that one doesn’t work either.

    • Niva says:

      Of course you can do it two standard pours. The solution is so simple. Too easy this week.

    • Ken Haley says:

      Ivan, there IS a solution for one of the 9 possible first moves. You’re missing it.

    • ctj says:

      actually, there are TWO solutions involving two pours (as you defined them).

    • Stevie says:

      There is a two pour solution. I couldn’t see it on Friday at all.
      A fresh look yesterday and I saw it immediately.

  29. veli says:

    can I make an assumption that “empty” and “pour” are 2 distinct actions?🙂

    • veli says:

      ah, finally got the 2 pour solution without the need for emptying anything!
      took a while though

  30. 10nuts says:

    Whoo hoo, got it. In case measuring one litre means having a bowl with just one litre in it.

  31. Oovavu says:

    If I’m honest, I’ve been thinking about it for about three hours. But I got there in the end. A completely no-trick, two-pour solution🙂

  32. Nasstasia says:

    It took a few mins but I was in a meeting had to take notes on unrelated matters at the same time.

    • Anne Elk says:

      I’m always impressed by anyone who can do these things in a minute or less! My brain obviously works in a different way. And in second gear.

  33. Heidi says:

    Love this. Took about a minute though to be fair I have seen something like it before.

  34. Dharmaruci says:

    i solved this prob but i did not notice how long it was took.

    i started at one end and imagined each possible pour from one bowl and then the possible second pour from any bowl. if that did not produce a soln i then imagined from another bowl. and finally the third.

    i did this three times as i obviously made a mistake. on the third time i found the soln also meantioned above.

    this is better puzzle then the few last ones.

  35. Physicalist says:

    Finally got it. Spent a few minutes stumped. Read comments to assure myself there is a legitimate answer. Then two minutes to click.

    No dumping/emptying. Bowls can be as fat as you like. No funny business.

  36. Tom says:

    Got it – about three hours after opening the web page, but about ten minutes of actually thinking about it.

  37. I tried to solve it this morning, but I had massive brain fog and I couldn’t hold in the information. This afternoon I came back and drew out each bowl labeling how much space is left and how full it is, and as soon as I did that the answer was very obvious and I got it straight away.

  38. Eddie says:

    Took a while but I got there.

  39. Anonymous says:

    Done in about a minute.

  40. Duncan says:

    A few minutes. Nice puzzle.

  41. Anonymous says:

    two seconds. Am I missing something?

  42. Anonymous says:

    mind block all day- come back this evening & still stalled but after a read of the comments to check i’m not missing something, i’ve gone back to it & got it! straight forward this week- no hidden clues or ambiguity.
    8 hours and 7 mins!

  43. Anonymous says:

    Got it in about a minute I think.

  44. Martha says:

    How on earth can you even pick up five litres of water, let alone start pouring it anywhere without spilling?

  45. Anonymous says:

    I got way off course with this one. I don’t know why the obvious solution eluded me at the start. I guess I thought I had checked all the simple solutions already, and then got into thinking about weird things like taking advantage of the Archimedes principle. I noticed it pretty quickly after I went back to test the simpler things again.

    • Mark_D says:

      It would be fun to devise one of these using Archimedes’ principle. Though you might have to make so many qualifications that it’ll point people to that solution… like with the old “3 light bulbs, 3 switches, check once problem”… now you have to point out that they’re incandescent light bulbs, which is kind of a giveaway.

    • Anon says:

      I’m with you here Anonymous. It took me way too looooooooooong to do this one even though I can normally solve these type of puzzles in a few seconds. I’m so embarrassed I remain anonymous too (although in fact I am a Canadian Atheist – calm down girls, form a queue).

  46. Dharmaruci says:

    there is also a cheat way of doing this.

    without giving the ans, imagine putting the five liter bottle into the eight. then remove it. you have transferred water because the five liter is now full. you have made no pourings.

    thus the initial circumstance is changed while yet two pourings are possible still.

  47. Hazel says:

    About five minutes of wrestling, then went back and had another look and took about ten seconds! Lovely and simple, 2 pours.

  48. MartinB says:

    3 answers to the problem, 2 pours each.
    1st answer was the simplest leaving 1L in C.
    2nd answer involved throwing away an amount of water leaving 1L in A. (One of the bowls was untouched)
    3rd answer involved marking a water level leaving 1L in B.
    10 mins total.

  49. Teun Spaans says:

    I got a tricky 2 x pouring solution in 1-2 minutes.

    For another weekly puzzle, see http://justpuzzles.wordpress.com/ (shameless plug, i admit)

  50. Got it, after quite a few attempts. The solution is easy to overlook and doesn’t require thinking outside the box or even the bowl.

  51. Louise says:

    Took about five minutes, but I’ve only just woke up.

    And I was distracted by the misspelling of “liter”.

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